What is a condensate pipe?
Modern condensing boilers produce acidic water as part of how they work. This condensate drains away through a plastic pipe, usually to a drain or soakaway. In many homes, part of this pipe runs outside, and in very cold weather the water inside can freeze. When that happens, the condensate cannot drain, and the boiler shuts down as a safety measure.
Signs your condensate pipe has frozen
- The boiler cuts out or will not fire up during a cold snap, while the rest of the house still has electricity and water
- You can hear gurgling or bubbling from the boiler or the pipe
- The boiler shows a fault or lock-out (the code varies by manufacturer, so check your manual)
- The external pipe is covered in ice, or the pipe or its end looks blocked by ice
How to thaw a frozen condensate pipe
Only do this if you can reach the pipe safely from the ground. Do not climb ladders in icy conditions. Never use boiling water or a naked flame. If you are unsure, call an engineer.
- Find the condensate pipe. It is a plastic pipe, usually 21.5mm or 32mm wide, running from the bottom of the boiler to a drain outside. The frozen part is usually on the outside, or at the open end or a bend.
- Pour warm water (not boiling) over the frozen section of the pipe. A kettle of hot water mixed with cold, or a watering can, works well. You can also hold a hot water bottle or warm cloth against the pipe.
- Take care with ice. The water can freeze on the ground, so be careful where you stand.
- Reset the boiler following the instructions in your manual. Many boilers have a reset button.
- Check that it restarts and that you can hear the condensate draining.
If the boiler still does not restart, the pipe may still be blocked, or there could be another problem. Check that the boiler pressure gauge is not reading low, and if you are still stuck, call us.
How to stop it freezing again
- Ask an engineer to insulate the external pipe with weatherproof lagging
- Have the pipe rerouted internally, or made wider, so less of it is exposed
- Make sure it has a proper fall and is not sagging, which allows water to collect
- Keep the end of the pipe clear of debris and leaves
An annual boiler service includes checking that the condensate pipe is clear and draining properly.
Frequently asked questions
Why does my boiler stop working when it is very cold?
A frozen condensate pipe is a common cause. When the pipe ices up, the condensate cannot drain and the boiler shuts itself down.
Can I use boiling water on a frozen condensate pipe?
No. Boiling water can crack plastic pipes and cause scalds, and it will refreeze on the ground. Use warm water.
Will thawing the pipe damage my boiler?
No. Thawing the pipe and resetting the boiler is a standard, safe step, as long as you follow your manual.
When should I call an engineer?
If thawing and resetting does not work, if the problem keeps coming back, or if you see leaks or smell gas. For gas smells, call 0800 111 999 straight away.
Prefer not to do it yourself, or not sure what is wrong? JR Plumbing and Heating covers Sheffield and the surrounding areas, with free, no-obligation quotes and a 24/7 emergency service. Call 07377 869384.